Machines such as, for example, dozers, motor graders, wheel loaders, wheel tractor scrapers, and other types of heavy equipment are used to perform a variety of tasks. Autonomously and semi-autonomously controlled machines are capable of operating with little or no human input by relying on information received from various machine systems. For example, based on machine movement input, terrain input, and/or machine operational input, a machine can be controlled to remotely and/or automatically complete a programmed task. By receiving appropriate feedback from each of the different machine systems during performance of the task, continuous adjustments to machine operation can be made that help to ensure precision and safety in completion of the task. In order to do so, however, the information provided by the different machine systems should be accurate and reliable. The velocity and distance traveled by the machine are parameters whose accuracy may be important for control and positioning of the machine.
Conventional machines typically utilize a navigation or positioning system to determine various operating parameters such as velocity, pitch rate, yaw rate, roll rate, etc. for the machine. Some conventional machines utilize a Distance Measurement Indicator (DMI) or odometer measurement to determine the velocity and distance traveled by the machine. For example, the machine controller may receive a measurement of the number of rotations of a wheel of the machine from the odometer and may calculate a distance traveled by the machine by using the number of rotations and a predetermined size of the wheel. The distance traveled may be utilized to determine the velocity of the machine. However, the distance calculated using the above method may have an error associated with it because the wheel size may change due to heat, tire pressure, road conditions, etc and the predetermined wheel size used to calculate the distance may not capture this wheel size change. Further, the rotations of the wheel may not accurately reflect the distance traveled if the wheels are subject to slipping. To compensate for such errors, some conventional machines utilize a scale factor for the distance calculation. In order to estimate the scale factor, an independent measurement for the distance traveled may be obtained by utilizing a Global Navigation Satellite System (GNSS). The distance calculated using GNSS data may be compared with the distance calculated using the odometer measurements and the scale factor may accordingly be adjusted to compensate for changes in wheel size due to the factors mentioned above.
An exemplary system that may be used to compensate for odometer measurement errors is disclosed in U.S. Pat. No. 6,360,165 (“the '165 patent”) to Chowdhary that issued on Mar. 19, 2002. The system of the '165 patent is capable of calculating the distance traveled by a vehicle. Specifically, the system of the '165 patent multiplies an odometer signal proportionate to the number of rotations of a drive train member (such as a wheel) with an odometer conversion parameter to convert the odometer signal into an estimated distance (Dr) traveled. When a Global Positing System (GPS) signal is available, a distance (Dg) traveled by the vehicle is calculated using the GPS signal and the odometer conversion parameter is calibrated to bring Dr into closer proximity to Dg. However, if the GPS signal is not reliable or the slip of the vehicle is higher than a certain threshold, the odometer conversion parameter is not updated to avoid introduction of slip related errors into the odometer conversion parameter.
Although the system of the '165 patent may be useful in determining the distance traveled by a machine, the system may not provide accurate estimates for distance traveled and velocity of the machine while dead-reckoning (i.e., during periods of time when GPS signals are unavailable) because the odometer conversion parameter is not updated during loss of GPS signals. For example, the system of the '165 patent may not compensate for any changes in the wheel size due to road conditions or weather conditions when the GPS signal is lost. In another scenario where the machine is loading or dumping materials carried by it while operating in an area where GPS signals are unavailable, a change in the wheel size is likely to occur but the system of the '165 patent may not compensate for this wheel size change because it does not update the odometer conversion parameter when GPS signals are unavailable.
The navigation system of the present disclosure is directed toward solving one or more of the problems set forth above and/or other problems of the prior art.